1. Field of the Invention
The present invention relates to an airbag device installed in a vehicle, and more particularly to a gas generator that supplies inflation gas to an airbag.
2. Related Technology
A vehicle such as an automobile is installed with an airbag system that rapidly inflates an airbag using gas in order to prevent an occupant from colliding with a dangerous location. The occupant is thus prevented from injury or death occurring when the occupant crashes into a hard part of the vehicle interior, such as a steering wheel or a windshield, during a collision, accident or the like. The airbag is structured to deploy when inflation gas is supplied thereto from a gas generator.
Patent Document 1, Japanese Patent Application Publication No. H5-317685, discloses an example of a conventional gas generator for an airbag.
This conventional gas generator uses three types of powder, namely an initiator that is ignited by an electric signal, an ignition powder igniter that promotes ignition of a gas generating agent by amplifying a flame generated by the initiator such that the flame is transmitted to the gas generating agent, and the gas generating agent for generating inflation gas. The three types of powder respectively have individual functions and are therefore accommodated or held in individual containers. As a result, the structure of the gas generator is complicated.
To solve this problem, a gas generator in which the ignition powder igniter is incorporated into the initiator has been proposed.
FIG. 3 is a sectional view illustrating an example (Patent Document 2, Japanese Patent Application Publication No. 2008-105618, for example) of the structure of a single stage type inflator 1. A housing 2 is constituted by a diffuser 2a, an adapter 2b, and a base 2c, and the following constitutional elements, for example, are accommodated in the housing 2.
An initiator 3 is ignited by an electric signal and a tube 4 separates the initiator 3 from a gas generating agent 7. Both the initiator 3 and the tube 4 are attached to the adapter 2b. A cup 6 houses an ignition powder 5 and is disposed inside the tube 4, and the ignition powder 5 in the cup 6 is burned by ignition energy from the initiator 3 causing thermal particles to pass through the entirety of the gas generating agent 7 such that a large amount of gas is generated instantaneously.
The generated gas passes through a filter 8, disposed along an inner peripheral side of an inner wall portion of the housing 2, bursts through aluminum foil 9 adhered to a gas ejecting hole 2aa provided in a side wall of the diffuser 2a, and is thus ejected from the gas ejecting hole 2aa so as to inflate the airbag.
The inflator having the above constitution uses three types of powder, namely the initiator, the ignition powder, and the gas generating agent, and these three types of powder respectively have individual functions. Therefore, individual containers must be provided to accommodate the three types of powder.
The amount of generated gas for inflating the airbag is determined by the amount of gas generating agent. Hence, in the inflator having the above constitution, a charging space for the gas generating agent is limited by a space corresponding to the volume of the ignition powder, the cup and the tube serving as a partition wall thereof. Accordingly, the gas generation amount is also limited.
As shown in FIG. 4, to solve the problem of requiring individual containers to accommodate the three types of powder, an inflator 1 that uses a large initiator 3 into which the ignition powder 5 is incorporated in advance and does not include a cup and a tube is available.
However, to ignite the gas generating agent sufficiently, a substantially identical amount of ignition powder to that of the inflator described above must be charged into the initiator. As a result, the size of the initiator becomes extremely large, and therefore the space for charging the gas generating agent remains limited.
A columnar agent or a hollow cylindrical agent is often used as the gas generating agent 7. A columnar gas generating agent is easy to manufacture and can be charged at a high density. As a result, a small, lightweight, and inexpensive gas generator can be obtained.
In the gas generator structured as shown in FIG. 4, a substantially identical amount of ignition powder to that of a conventional ignition powder igniter must be charged into the initiator 3 to ensure that the gas generating agent 7 is ignited sufficiently, and therefore the size of the initiator must be increased greatly. Hence, the structure and manufacturing process of the initiator 3 become complicated, leading to an increase in cost.
Incidentally, a powder that generates a large amount of combustion heat, such as boron potassium nitrate, strontium nitrate, or magnesium Teflon, is selected as the ignition powder. However, when these types of powder are used as the ignition powder charged into the large initiator, the gas generating agent may begin to burn after combustion of the ignition powder, and therefore a time delay may occur before gas is discharged from the inflator.